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(11) | EP 0 643 799 B1 |
| (12) | EUROPEAN PATENT SPECIFICATION |
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| (54) |
MUFFLER WITH CATALYTIC CONVERTER ARRANGEMENT SCHALLDÄMPFER MIT ANORDNUNG EINES KATALYTISCHEN UMWANDLERS SILENCIEUX AVEC DISPOSITIF CONVERTISSEUR CATALYTIQUE |
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| Note: Within nine months from the publication of the mention of the grant of the European patent, any person may give notice to the European Patent Office of opposition to the European patent granted. Notice of opposition shall be filed in a written reasoned statement. It shall not be deemed to have been filed until the opposition fee has been paid. (Art. 99(1) European Patent Convention). |
Field of the Invention
[0001] The present invention relates to muffler assemblies and in particular to muffler assemblies of a type used to dampen exhaust noise produced by internal combustion engines. The invention specifically concerns such arrangements having catalytic converters therein.
Background of the Invention
[0002] Catalytic converters have been widely utilized with internal combustion engines, typically gasoline powered engines. In operation, an oxidizing catalytic converter comprises a post combuster through which emissions from the internal combustion process are directed. The catalyst promotes the conversion of carbon monoxides and hydrocarbons in the emissions to carbon dioxide and water vapor.
[0003] In a typical application, the catalytic converter is located in the exhaust system as close to the exhaust engine manifold as practical. In this manner, advantage is taken of available heat in the exhaust gases to minimize the time lag in reaching the desired operating (reaction) temperature. The typical catalyst is a noble metal such as platinum or palladium.
[0004] As indicated above, typically catalytic converters have been utilized with gasoline powered internal combustion engines, rather than diesel engines such as truck engines. There are numerous reasons for this. For example, trucks typically have very limited space for the placement of catalytic equipment in the exhaust system. The largest space available is occupied by the muffler, leaving little if any room for effective placement of a catalytic converter. It is not generally reasonable to reduce the size of the muffler to allow for placement of a converter assembly. This is because reduction in the size of the muffler will generally lead to less sound attenuation and higher backpressure.
[0005] In addition, in a diesel powered truck system the acceptable amount of resistance to flow in the exhaust stream is strictly limited. More specifically, an effective muffler system for a diesel engine truck typically provides a backpressure close to the maximum backpressure allowable for efficient engine use. The added backpressure which would be introduced by placement of a conventional catalytic converter arrangement in the exhaust stream (in addition to the conventional muffler) would typically be unacceptably close to (if not over) the maximum backpressure allowable and would reduce fuel efficiency.
[0006] Nevertheless, there are reasons why it may be desirable to introduce a catalytic converter into a diesel exhaust flow stream. In particular, the catalyst allows for the oxidation of hydrocarbons in the gaseous phase, thereby reducing the concentration of hydrocarbons in the exhaust stream. Due to the concentration reduction, a lower amount of hydrocarbons would be adsorbed onto the surface of carbonaceous particles or soot in the stream. Thus, there will be a mass reduction in the tailpipe emissions, if a catalytic converter can be efficiently utilized.
[0007] Apparatus comprising muffler arrangements with an outer shell and exhaust inlet and an exhaust outlet, and further including means for sound attenuation position within the shell, are known, see for example WO 89/01566.
Summary of the Invention
[0008] According to the present invention an apparatus according to claim 1 is provided for modifying an exhaust stream of an engine. Herein the term "modifying" in this context is meant to refer to the conduct of at least two basic operations with respect to the exhaust stream: sound attenuation (muffling); and, catalytic conversion (catalyzed combustion of hydrocarbons in the exhaust gas stream). In typical preferred applications the apparatus is utilized for the modification of an exhaust stream of a diesel engine. In most typical applications, the apparatus is utilized as a muffler arrangement for the diesel engine of a vehicle, such as an over-the-highway truck.
[0009] The apparatus according to the present invention comprises a muffler arrangement, a catalytic converter arrangement and flow direction means. The muffler arrangement generally has an exhaust inlet, exhaust outlet and means for sound attenuation. That is, exhaust gas is passed through the muffler arrangement from the inlet through to the outlet, with sound attenuation occurring within the muffler.
[0010] The catalytic converter arrangement is preferably positioned within the muffler arrangement in the gas flow stream between the exhaust inlet and the exhaust outlet. In general it is operatively positioned such that as exhaust gas is passed through the muffler arrangement, it is passed through the catalytic converter. The catalytic converter is constructed and arranged such that in use it will effect a catalyzed conversion in the exhaust gas flow stream, i.e., oxidation of hydrocarbon components in the exhaust gas flow.
[0011] The means for flow direction generally comprises means directing the exhaust gases through the catalytic converter arrangement whenever the gases operably flow through the muffler arrangement from the exhaust inlet to the exhaust outlet. In a typical system this means comprises appropriate construction and configuration for the apparatus so that gas flow cannot bypass the catalytic converter arrangement while passing through the muffler.
[0012] A variety of arrangements may be utilized as the means for sound attenuation. Among them are included arrangements utilizing one or more resonating chambers for sound attenuation, within the muffler. Resonating chambers may be positioned both upstream and downstream of the catalytic converter arrangement. In typical constructions, substantial use would be made of downstream resonating chambers (or other downstream acoustic elements) to achieve substantial sound attenuation.
[0013] In one preferred apparatus, the means for sound attenuation includes a "sonic choke" arrangement operably positioned within the muffler arrangement, as part of the downstream acoustics. In general, a sonic choke arrangement comprises a tube having a converging portion to a neck, with an expanded flange on an end thereof. The expanded flange is positioned on the most upstream end of the sonic choke, with the shape of the choke or tube converging rapidly from the flange to a narrowest portion in the neck, and then with a relatively slow divergence in progression from the neck toward the exhaust outlet.
[0014] In the selected arrangement according to the present invention the catalytic converter arrangement is operatively positioned between an exhaust inlet and the downstream acoustics. The catalytic converter may comprise a metal foil core having an effective amount of catalyst dispersed thereon. In this context the term "effective amount" is meant to refer to sufficient catalyst to conduct whatever amount of conversion is intended under the operation of the assembly. The term "dispersed thereon" is meant to refer to the catalyst operably positioned on the catalytic converter core, regardless of the manner held in place.
[0015] When the catalytic converter arrangement comprises a metal foil core, generally the core comprises corrugated foil coiled in arrangement to form a porous tube having an outer surface. In the preferred arrangement, the outer surface is generally cylindrical and an outer protective sheet such as a metal sheet may be positioned around the core outer cylindrical surface. Preferred metal foil cores have a cell density, i.e., population density of passageways therethrough, of at least about 31 cells/cm2 and more preferably about 62 cells/cm2. Such an arrangement can be formed from corrugated stainless sheeting of about 0.04 mm (0.025 - 0.076 mm) thick.
[0016] A variety of catalysts may be utilized in assemblies according to the present invention including platinum, palladium, rhodium and vanadium.
[0017] In certain alternate embodiments the catalytic converter core may comprise a porous ceramic core. A typical such core will be formed from extruded cordierite (a magnesia alumina silicate) and have an effective amount of catalyst dispersed thereon. Preferably the cell density of passageways through such a ceramic core is at least about 31 cells/cm2 and preferably at least about 62 cells/cm2.
[0018] In preferred arrangements wherein the catalytic converter core comprises ceramic, the ceramic core is provided in a generally cylindrical configuration, with an outer cylindrical surface. The ceramic core is preferably protected by the catalytic converter arrangement being provided with a flexible, insulating mantle wrapped around the core outer surface. The insulating mantle will preferably be secured in place by the positioning of an outer metal wrap therearound. In preferred arrangements the outer metal wrap is provided with side flanges, operably folded over upstream and downstream faces of the catalytic converter core. Preferably a soft, flexible insulating rope gasket is positioned adjacent any such folds or flanges, to inhibit crumbling of the ceramic core during the manufacture and installation process and to provide a seal for the less durable insulating mantle materials.
[0019] Preferred arrangements according to the present invention include a flow distribution arrangement constructed and arranged to direct the exhaust flow substantially evenly against the catalytic converter. In particular, the catalytic converter core member may be described as having a most upstream face. Preferably the flow distribution element is constructed and arranged to direct flow relatively evenly across the upstream face of the catalytic converter core member. In one preferred embodiment, which is described and shown, the flow distribution element comprises a porous tube having an end with a "star crimp", i.e. a type of folded end closure, therein. In another, a domed, perforated baffle member positioned between the exhaust inlet and the porous core member upstream face serves as a flow distribution element. In still another, curved surfaces are used to generate a radial diffuser inlet.
[0020] It has been determined that there is a preferred positioning of the porous core member between the flow distribution element and the downstream acoustics. More specifically, preferably the porous core member is positioned within about 25.4 mm to 152 mm from the flow distribution element; and, preferably the core member is also positioned within about 25.4 mm inch to 152 mm from the re-entrant tube inlet for the downstream acoustics. Also, a preferred open area fraction for the flow distribution element can be defined. Detailed descriptions with respect to this are provided herein below.
[0021] In addition, according to the present invention an apparatus for providing a relatively even fluid (typically gas) flow velocity across a conduit (typically having a substantially circular cross section) is provided. In general the apparatus is adapted for generating even flow in a situation in which gases pass into an arrangement through an inlet tube having a first diameter (cross-sectional size) to a chamber having a second diameter (cross-sectional size) greater than the first diameter. Typically, a domed perforated diffusion baffle having a second diameter greater than the first (inlet) diameter, is located downstream from the inlet tube. What is needed, is an arrangement to provide for direction of gases against the domed perforated diffusion baffle in such a manner that as the fluid or gases pass therethrough, an even flow distribution (i.e. velocity of gases or volume of gases directed against almost any point in cross section) is provided. This is accomplished by positioning a bell shaped radial diffuser element upstream from the domed perforated diffusion baffle and downstream from the inlet tube. The bell shaped radial diffuser element generally comprises an expanding bell having a shape similar to the bell of a musical instrument. Preferred sizes and curvatures are described herein. In general the bell allows for expansion of the gases as they approach the dome perforated diffusion baffle for even flow distribution. Such arrangements may be utilized in a variety of muffler constructions including ones having catalytic converters therein.
[0022] The present invention concern arrangements wherein the muffler is provided with both the gas flow inlet and the gas flow outlet on (or adjacent) one end of the muffler. The catalytic converter core for such an arrangement is positioned downstream from the inlet, with appropriate flow directing means directing exhaust gases through the catalytic converter core in a downstream direction, and then back past the converter core toward the exhaust outlet. In the arrangement described and shown, an annular backflow around (or across) an exterior periphery of the catalytic converter core is provided, to accomplish this.
Brief Description of the Drawings
[0023] Fig. 1 is a schematic cross-sectional view of a muffler assembly integral with a catalytic converter arrangement therein.
[0026] Fig. 4 is a schematic cross-sectional view of a muffler assembly with a catalytic converter arrangement therein according to the present invention; in Fig. 4, the muffler assembly having an inlet and outlet generally adjacent a single end of the muffler shell, and a catalytic converter arrangement generally analogous to that shown in Figs. 1, 3, and 4.
Detailed Description of the Invention
[0028] As required, a detailed description of different embodiments is presented herein. The description provided is not intended to be limiting.
The General Configuration of the Overall Assembly
[0029] A first embodiment shown in Figs 1-3 does not form any part of the invention but is included herein as reference to provide a fuller understanding of the invention.
[0030] The reference numeral 1, Fig. 1 generally designates a muffler assembly integral with a catalytic converter. The muffler assembly 1 has defined therein three general regions: an exhaust introduction, distribution and upstream acoustics region 5; a catalytic converter region 6; and a downstream acoustical or attenuation region 7. Each of regions 5, 6 and 7 may be constructed separately, with the overall assembly prepared through utilization of appropriate clamps, segments, etc. However, in applications as shown in Fig. 1, it is foreseen that the segments 5, 6 and 7 will be constructed in an overall unit 10 having an outer shell 11 with no segment seams or cross seams therein. By "cross seam" in this context it is meant that the shell 11 is not segmented into longitudinally aligned segments, rather it comprises one longitudinal unit, typically (but not necessarily) having at least one and possibly more than one longitudinal seam.
[0031] Herein a unit 10 which is constructed with no cross seams, i.e., as a single longitudinal unit, will be referred to as an "integrated" unit. To a certain extent, it may be viewed as a muffler assembly having a catalytic converter positioned operably therein. A unit constructed in segments aligned coaxially and joined to one another along cross seams will be referred to as a "segmented" arrangement. It will be understood that to a great extent the principles of the present invention may be applied in either "integrated" or "segmented" units or arrangements. It is an advantage of the preferred embodiment of the present invention, however, that they are well adapted for arrangement as "integrated" units.
[0032] As will be understood from the following descriptions, the muffler assembly 1 is constructed to operate effectively and efficiently both as an exhaust noise muffler and as a catalytic converter. With respect to operation as an exhaust noise muffler, many of the principles of operation are found in, and can be derived from, certain known muffler constructions. With respect to these principles, attention is directed to U.S. Patents 3,672,464; 4,368,799; 4,580,657; 4,632,216; and 4,969,537.
[0033] Still referring to Fig. 1, muffler assembly 1 comprises a cylindrical casing or shell 11 of a selected predetermined length. Annular end caps 13 and 14 respectively define an inlet aperture 17 and an outlet aperture 18. The shell 11 is generally cylindrical and defines a central longitudinal axis 20. An inlet tube 22 is positioned within inlet aperture 17. The inlet tube 22 has a generally cylindrical configuration and is aligned with its central longitudinal axis generally coextensive or coaxial with axis 20. It is noted that end portion 24 of inlet tube 22 is configured in a manner non-cylindrical and described in detail hereinbelow, for advantage.
[0034] Outlet tube 26 is positioned within outlet aperture 18. Outlet tube 26 includes a generally cylindrical portion 27 aligned with a central longitudinal axis thereof extending generally coextensive with or coaxially with longitudinal axis 20.
[0035] In use, the exhaust gases are directed: (1) into assembly 1 by passage through inlet tube 22 as indicated by arrows 30; (2) into the internal region or volume 31 defined by casing or shell 11; and, (3) outwardly from assembly 1 by passage outwardly through outlet tube 26 as indicated by arrows 33. Within assembly 1 both sound attenuation (muffling) and emission improvement (catalytic conversion) occur.
[0036] Referring to region 5, and in particular inlet tube 22 positioned therein, the inlet tube 22 is positioned and secured in place by end cap 13 and internal baffle 35. Preferably baffle 35 is constructed so as not to be permeable to the passage of the exhaust gases therethrough or thereacross. Thus, baffle 35 in cooperation with end cap 13 and shell 11 define a closed volume 37.
[0037] For the arrangement shown in Fig. 1, inlet tube 22 is perforated along its length of extension within assembly 1, i.e., that portion of the tube 22 positioned internally of end cap 13 (that is positioned between end cap 13 and end cap 14) is perforated, as indicated by perforations 38. Certain of the perforations allow gas expansion (and sound travel) into volume 37, which assists in attenuation of sound to some degree. Regions such as volume 37 may be generally referred to as "resonating chambers" or "acoustics", and similar structure positioned upstream of region 6 and also constructed and arranged for sound attenuation, will be referred to herein as "upstream acoustics."
[0038] The portion 42 of inlet tube 22 which projects inwardly of baffle 35; i.e., which extends over a portion of the volume between baffle 35 and outlet end cap 18, operates as a flow distribution construction or element 44. The flow distribution element 44 generates distribution of exhaust gas flow within volume 45, i.e., the enclosed volume of shell 11 positioned immediately inwardly of baffle 35, for advantage. Portion 42 of inlet tube 22 includes previously defined end portion 24.
[0039] Positioned immediately downstream of inlet tube 22 is catalytic converter 50. Catalytic converter 50 includes a substrate 51 having catalyst appropriately positioned thereon. The substrate 51 is gas permeable, i.e., the exhaust gases pass therethrough along the direction of arrow 53. The catalytic converter 50 includes sufficient catalyst therein to effect the desired conversion in the exhaust gases as they pass therethrough. Herein this will be referred to as "an effective amount" of catalyst. The substrate 51 is sized appropriately for this. Greater detail concerning the preferred catalytic converter 50 is provided hereinbelow.
[0040] Preferably the flow distribution element 44 is sized and configured appropriately to substantially evenly distribute exhaust flow against the entire front or upstream surface 55 of the catalytic converter 50. In this manner, lifetime of use in the catalytic converter 50 is enhanced. Also, the more effective and even the distribution, the less likelihood of overload in any given portion of the catalytic converter 50. This will facilitate utilization of a catalytic converter minimal or relatively minimal thickness, which is advantageous. By the term "substantially evenly" in this context it is meant that flow is distributed sufficiently to avoid substantial "dead" or "unused" volume in converter 50. Generally, as even a distribution as can be readily obtained, within acceptable backpressure limits is preferred.
[0041] In general, the catalytic converter 50 provides for little or no sound attenuation within the muffler. Thus, the space utilized by the catalytic converter is space or volume of little or no beneficial effect with respect to muffler operation. Under such conditions, minimal thickness or flow path catalytic converter will be preferred, so as not to substantially inhibit muffler (attenuation) operation.
[0042] It has been determined that there is a preferred positioning of the catalytic converter 50 relative to the flow distribution element 44, for advantageous operation. In particular, most preferred operation occurs when the catalytic converter 50 is not positioned too close to the flow distribution element 44, but is also not positioned too far therefrom. A discussion of studies with respect to optimizing the position of the catalytic converter 50 relative to the flow distribution element 44 is provided hereinbelow, in detail.
[0043] For the arrangement shown in Fig. 1, flow distribution element 44 comprises end 24 of tube 22 crimped or folded into a "star" or "four finned" configuration. Such an arrangement has been used in certain types of muffler assemblies before, see for example Wagner et al. US-A-4 969 537 referred to above. In general, the crimping creates closed edges 56 and facilitates flow distribution. Unlike for conventional muffler arrangements, for the embodiment of Fig. 1 this advantageous distribution is applied in order to achieve relatively even cross-sectional distribution of airflow into and through a catalytic converter 50, to advantage. As will be understood from alternate embodiments described hereinbelow, alternative flow distribution arrangements may be utilized in some applications.
[0044] The portion 60 of the muffler assembly 1 in extension between the downstream surface 61 of the catalytic converter 50 and the outlet end cap 14 is referred to herein as the downstream acoustical or attenuation segment or end 7 of the assembly 1. It is not the case that all sound attenuation which occurs within the assembly 1 occurs within this region. However, the majority of the sound attenuation will occur in this portion of the assembly 1.
[0045] In general, the downstream acoustical segment 7 comprises structure placed to facilitate sound attenuation or sound control. In typical constructions, resonating chambers or the like will be included therein. One such construction is illustrated in Fig. 1. The particular version illustrated in Fig. 1 utilizes a sonic choke arrangement 65 therein in association with resonating chambers, to achieve sound attenuation. It will be understood that a variety of alternate arrangements may be utilized.
[0046] Referring more specifically to Fig. 1, acoustical or attenuation segment 7 includes therein a converging or sonic choke arrangement 65 supported by sealed baffle 66. In general, the volume 68 upstream from sealed baffle 66 will be constructed or tuned for advantageous low frequency sound attenuation. Such tuning will in general concern the precise location of the sealed baffle 66, i.e., adjustment in the size of volume 68. Constructions in which a sonic choke assembly similar to that illustrated as 65 are positioned within a muffler assembly 1 by a sealed baffle 66 advantageously, are described in U.S. Patents 3,672,464 and 4,969,537.
[0047] In general, sonic choke assembly 65 comprises a tube member 75 mounted coaxially with outlet tube 26 and, together with outlet tube 26, supported by baffles 66 and 77, and outlet end cap 18. In certain constructions such as that shown in Fig. 1, tube member 75 may comprise an extension of an overall tube, having no cross seam, which includes both the tube member 75 and the outlet tube 26 as portions thereof. Alternately stated, for the embodiment shown in Fig. 1, the outlet tube 26 comprises an end portion of tube member 75. In the alternative, the outlet tube 26 may comprise a separate extension of material from tube member 75; the outlet tube and tube member being joined along a cross seam such that they are oriented substantially coaxial with one another.
[0048] For the embodiment shown, the tube member 75 defines a central longitudinal axis positioned generally coextensive and coaxial with axis 20. In some constructions, a tube member 75 with a longitudinal axis off-set from alignment with the inlet axis may be used.
[0049] Still referring to Fig. 1, tube member 75 in combination with outlet tube 26 defines exit flow for exhaust gases passing along the direction of arrow 53 through catalytic converter 50. More specifically, such gases pass through an interior 80 of the tube member 75 and outwardly through outlet tube 26, as indicated at arrows 33.
[0050] Between baffles 66 and 77, and externally of tube member 75, a volume 85 is defined within shell 11. An extension 88, of the combination of tube member 75 and outlet tube 26 extending through volume 85, is perforated as shown by perforations 84, to allow for expansion of gases into volume 85. Volume 85 will operate as a resonator or resonating chamber for attenuation of sound, in particular continued attenuation of low frequency and much of the medium frequency attenuation. The size of the volume 85 may be selected so that it is tuned for preferred sound attenuation including some high frequency attenuation as well.
[0051] Similarly, between baffle 77 and end cap 14 chamber 90 is defined, externally of tube member 75 and outlet tube 26, and internally of shell 11. The portion 91 of outlet tube 26 extending between baffle 77 and end cap 14 is perforated, to allow expansion of gases (and leakage of sound waves) into volume 90. The size and configuration of volume 90 may be tuned for selected medium and high frequency sound attenuation.
[0052] Still referring to Fig. 1, tube member 75 includes a conical end 92 which converges from point 93 to neck 94, i.e., it converges in extension toward the catalytic converter. On the opposite side of neck 94 from point 91, the tube member 75 diverges at flange 95 to lip 96; lip 96 defining a re-entry port for gasses passing through assembly 1. Such a construction is advantageous for preferred muffler operation and sound attenuation. As indicated above, such a construction is referred to herein as a sonic choke. Sonic chokes are described generally in Rowley et al. U.S. Patent 3,672,494.
[0053] In general, a portion of the sound waves existing in the gaseous medium of volume 31 are inhibited from passing through the tube member 75 by increased acoustical impedance encountered at the narrow neck 94. Such waves are reflected back, which serves to attenuate the sound level.
The Construction of the Catalytic Converter
[0054] As indicated generally above, a variety of constructions may be utilized for the catalytic converter 50. One such construction is illustrated in Figs. 1 and 3.
[0055] For the arrangement of Figs. 1 and 3, the catalytic converter 50 comprises a ceramic structure having a honeycomb-like configuration defining a plurality of longitudinal flow channels extending therethrough. Referring to Fig. 3, the ceramic construction (or core) is indicated generally at 100. For mounting within the assembly 1, the ceramic core 100 is provided in a circular configuration, i.e., core 100 defines a cylindrically shaped item. Although alternate configurations are possible, the cylindrical one described and shown is advantageous for positioning within a cylindrical shell 11.
[0056] A ceramic cylinder having a large plurality of longitudinal channels extending therethrough is a somewhat brittle configuration. It is therefore preferably mounted such that it will be dampened from the shocks and vibrations generally associated with a muffler assembly in a diesel powered vehicle. For the arrangement of Figs. 1 and 3, the ceramic core 100 is provided with a dampening mantle or wrap 101 in extension around an outer periphery 102 thereof. The mantle 101 should be provided from a flexible, heat resistant material, such as a vermiculite pad. The material Interam® Mat III available from 3M, St. Paul, Minnesota 55144 is usable. In general, for the arrangement shown the mantle 101 would be about 0.12 in. (0.3 cm) to 0.25 in. (0.64 cm) thick.
[0057] For the preferred embodiment, the mantle 101 is retained against the core 100 by retaining means such as a cylindrical casing 105 of sheet metal. Preferably the casing 105 is provided not only in extension around the outside of the mantle 101, but also with a pair of side flanges bent toward the front face 55 and rear face 61, respectively, of the core 100 to contain the mantle 101. That is, casing 105 has first and second side lips or rims 106 and 107 folded toward opposite sides of the core 100. Preferably a circular loop of rope or O-shaped gasket 109 is provided underneath each of the rims 106 and 107, to facilitate secure containment of the core 100 and mantle 101 within the casing 105, without damage.
[0058] Referring to Figs. 1 and 3, it will be understood that the preferred catalytic converter 50 illustrated is a self-contained or "canned" unit, positioned within shell 11. The converter comprises a ceramic core 100 positioned within a casing 105, and protected therein by the mantle 101 and rope rings 109. The converter 50 can thus be readily welded or otherwise secured and placed within shell 11, with good protection of the core 100 from extreme vibrations within the assembly 1. In addition, the mantle 101 and rings 109 will help protect the converter 50 from premature deterioration due to flow erosion.
[0059] In a typical system, it is foreseen that the ceramic core 100 will comprise an alumina magnesia silica (crystalline) ceramic, such as cordierite, which has been extruded from a clay, and then dried and fired to a crystalline construction. Techniques for accomplishing this are known in the ceramic arts. In many, crystalline ceramics are prepared as catalytic converter cores by application of a wash coat thereto and then by dipping the core into a solution of catalyst. In some, the wash coat and catalyst are applied simultaneously. Typical catalysts utilized would be noble or precious metal catalysts, including for example platinum, palladium and rhodium. Other materials such as vanadium have also been used in catalytic converters.
[0060] In general, for use within a diesel engine muffler assembly, it is foreseen that the core 100 should be extruded with a cell density of longitudinal passageways of 31 cells/cm2 to 193 cells/cm2 and preferably at least about 62 per cm2 (400 per square inch) of front surface area.
Size of the Catalytic Converter and its Positioning relative to the Downstream Acoustics and Flow Distribution Element
[0061] In general, catalyst activity is a function of temperature. That is, a catalytic converter generally operates best when it is hottest(withindesignlimits). Thus, since the inlet end of a muffler assembly is hotter than the outlet end, it is generally preferable to position the catalytic converter toward the inlet end of the arrangement to the extent possible. Thus, for the arrangement shown in Fig. 1 the catalytic converter is generally positioned adjacent the flow distribution element.
[0062] However, if the catalytic converter is positioned too close to the flow distribution element, inefficient use will result, due to inefficient spread of flow across the front surface of the catalytic converter. In general it is foreseen that for diesel engine truck muffler assemblies the catalytic converter will be generally preferably positioned within a distance of about 2-4 inches (5-10 cm), preferably about 2.0-3.0 inches (5-7.5 cm) and most preferably around 2.0 inches (5.0 cm) from the flow distribution element. The results of some simulated modeling and calculations with respect to this are presented hereinbelow.
[0063] Also, in general the catalytic converter takes up space in the muffler assembly otherwise utilizable for low-frequency sound attenuation. Since the catalytic converter does not facilitate sound attenuation and since sound attenuation will not generally take place in the space occupied by the catalytic converter, a problem with the catalytic converter positioning is that it interferes with sound attenuation. It is desirable, therefore, to render the catalytic converter as short as reasonably possible. This is facilitated by assuring good flow distribution across the front surface of the catalytic converter, as indicated above, and also by positioning the catalytic converter where it will operate at the hottest and thus most efficient. In general it is foreseen that a catalytic converter utilizable in assemblies according to the present invention (as converters in muffler assemblies for diesel trucks) will need to be about 3.0-8.0 inches (7.6-20.3 cm) long and generally preferably about 5.0-6.0 inches (12.7-15.2 cm) long. It is foreseen that, therefore, in preferred constructions according to the present invention (for diesel engine mufflers) the muffler assembly will be about 5.0-6.0 inches (12.7-15.2 cm) longer than would a muffler assembly not having a catalytic converter positioned therein but utilized to achieve the same level of sound attenuation in a diesel engine exhaust stream.
[0064] To improve efficiency, and thus shorten the length of core needed, it is also preferred that the population density of pores through the core be as high as reasonably obtainable. Thus, high porosity (with a large population of very small pores) is generally preferred.
[0065] As indicated generally above, it is preferred that the catalytic converter be integrated with the muffler assembly, i.e., positioned therein, rather than positioned simply in a flow stream in series with a muffler assembly. The reasons for this include that it is foreseen that less overall backpressure will be generated by such a system.
The Embodiment of Figs. 4 and 5
[0066] An embodiment of an arrangement according to the present invention is depicted in Figs. 4 and 5. In general, the embodiment of Figs. 4 and 5 concerns a muffler assembly wherein exhaust gas inlets and outlets for the muffler assembly are positioned on, or adjacent, a single end of the muffler shell.
[0067] Referring to Fig. 4, an assembly 500 is generally depicted. Muffler assembly 500 comprises a shell 502 having an exhaust gas flow inlet 503 and an exhaust gas flow outlet, 504. In general, then, exhaust flow from an engine is directed into assembly 500 along a general direction of arrow 506. Within assembly 500, sound attenuation and catalytic conversion are conducted. Exhaust gas then exits assembly 500 along the path indicated by arrow 507.
[0068] Exhaust gas flow through assembly 500, between inlet 503 and outlet 504 is generally indicated by arrows 509. The path of flow is dictated by flow directing means, as described. Along the path flow, the exhaust gases are directed through catalytic converter assembly 512. The particular arrangement 512 depicted comprises core 513 surrounded by mantle 514 and casing 515. Core 513 has an upstream face 517 and a downstream face 518. In general, normal exhaust gas flow during operation of assembly 500 is through core 513 from the upstream face 517 toward the downstream face 518.
[0069] The arrangement according to Figs. 4 and 5 is generally distinguished from arrangement according to Fig. 1, by the relative locations of the inlet 503 and outlet 504 with respect to the catalytic converter assembly 512. For the arrangement of Fig. 4, the inlet 503 and outlet 504 are positioned in shell 502 at locations on the same side of core 513 as the upstream face 517. For the arrangement shown in Fig. 1, the inlet 22 and outlet 26 were positioned in shell 11 on opposite sides of catalytic converter 50. In addition, flow through the outlet of the embodiment of Fig. 4 is generally orthogonal to flow through the inlet; whereas for Fig. 1, flow through the outlet is generally parallel, and preferably coaxial, to flow through the inlet.
[0070] A purpose for depiction of the embodiment shown in Figs. 4 and 5 is to illustrate how a muffler assembly 500 having the inlet 503 and outlet 504 positioned adjacent to the same end of the shell 502 can be adapted for utilization with a catalytic converter assembly 512 according to the present invention.
[0071] Referring again to Fig. 4, inlet 503 comprises inlet tube 520 positioned within end 521 of shell 502, by end cap 523 and baffle 524. Both end cap 523 and baffle 524 are solid, except for central apertures 526 and 527, respectively, therein to allow extension of inlet tube 520 therebetween. Inlet tube 520 is solid, not perforated, in region 529 extending between end cap 523 and baffle 524. A reason for this is to prevent escape of inlet gases into volume 530, between end cap 523 and 524. Such an escape would allow exhaust gas flow to bypass catalytic converter assembly 512 as it is directed to outlet 504.
[0072] On a downstream side 531 of baffle 524, inlet tube 520 is provided with an inlet diffuser construction 532. For the arrangement shown in Fig. 4, inlet diffuser construction 532 comprises an extension 533 of tube 520 having perforations 534 therein and a domed, solid, nonperforated end cap 535 positioned in an outlet end 536 of extension 533. As a result of perforations in extension 533, the exhaust gases will flow outwardly from inlet diffuser 532 and expand into volume 540, as they pass through assembly 500. The perforations 534 also allow for escape of sound from tube 520.
[0073] Volume 540 is in general defined by baffle 524, upstream face 517 of catalytic converter assembly 512, and internal shell 542. For the assembly 500 described as shown, internal shell 542 comprises a cylindrical extension 543 having a smaller cross-sectional area than shell 502. Extension 543 is positioned within shell 502 with annular space 544 extending therearound. Spacers 546 position shell 542 within assembly 500 spaced from shell 502. Spacers 546 may comprise a variety of arrangements. For the particular embodiment shown in Figs. 4 and 5, spacers 546 comprise U-channels 547. Catalytic converter assembly 512 is supported within internal shell 542 in a manner analogous to the way the catalytic converter assembly 50 was supported within shell 11, Figs. 1 and 3.
[0074] Volume 540 comprises an expansion volume which will operate in part as an acoustic attenuator (upstream acoustics), to muffle sound. The geometry and dimensions of volume 540 may be selected to achieve a preferred amount of sound attenuation, utilizing known muffler tuning techniques. Generally it is anticipated that the nature of attenuation occurring in volume 540 will be similar to that occurring in volume 68, Fig. 1, i.e. low frequency and middle frequency attenuation to the greatest degree, with some high frequency attenuation.
[0075] After passing through volume 540, the exhaust gases are directed through catalytic converter core 513 into volume 549. Volume 549 represents an expansion chamber for the exhaust gases. Within volume 549, further attenuation occurs. The size and shape of volume 549 can be tuned to achieve a preferred amount of acoustical attenuation.
[0076] Assembly 500 is provided with internal baffle 551 and end cap 552. Both are preferably solid, not perforated. Internal baffle 551 is provided with central aperture 555 having tube 556 extending therethrough. Tube 556 has a re-entry port 557 on an end thereof adjacent converter 512. Port 558 is provided on an opposite end of tube 556. Baffle 551 and end cap 552 define volume 559, within assembly 500.
[0077] Internal baffle 551, end cap 552, tube 556 and volume 559 comprise an acoustical attenuator or resonating chamber 560. The tube 556, then, extends between resonating chambers 549 and 560. The size and geometry of the chamber 560, as well as the shape of baffle 551 end cap 552 and the size, shape and length of tube 556, may be tuned or selected for preferred amount of sound attenuation within assembly 500. It is anticipated that in general, medium and high frequency attenuation will be conducted, within volume 559.
[0078] Exhaust gas flow outwardly from assembly 500 will now be apparent. Upon exiting volume 549, the gas flow is directed through annular space 544, between internal shell 542 and the exterior shell 502. The exhaust gas flow is then directed in an annular fashion past converter core 513 (i.e., around an outer periphery 561 thereof into volume 530, and outwardly through outlet tube 562.
[0079] Referring to Fig. 5, the annular space 544 comprises an exhaust flow annulus which includes flow spaces 563, within U-channels 547 and flow spaces 564 between the U-channels 547. It will be understood that alternate spacers 546 (to U-channels 547) could be selected, which would not be hollow to allow gas flow to go through.
[0080] Arrangement 500 may be constructed of a variety of materials. In general, sheet metal may be utilized for internal components, tubes, baffles and the like, as for conventional muffler constructions. Catalytic converter assembly 512, again, may be according to any of the variations described hereinabove with respect to other embodiments.
[0081] The embodiment of Figs. 4 and 5 will be highly advantageous for certain applications. In many truck systems, it is desirable to have a muffler assembly with the inlet and outlet positioned adjacent a single end thereof. A limited amount of space or volume may be available, for positioning of the muffler assembly. If a catalytic converter is to be positioned within that muffler assembly, it must be designed such that appropriate exhaust gas flow will occur, without undue back pressure.
[0082] In general, the operation of a catalytic converter core is a function of its volume. Efficiency of conversion can be improved by either increasing depth, increasing cross-sectional area, or both. A problem with increasing depth is that a greater amount of friction to exhaust gas flow therethrough is provided, thus the cbre becomes a greater and greater restriction to exhaust gas flow (resulting in increasing back pressure). The arrangement shown in Figs. 4 and 5 allows for a substantial cross-sectional area of the catalytic converter core 513 within a given volume for a muffler assembly shell 502.
[0083] As indicated previously, efficiency of catalytic converter operation is also a function of temperature. The hot gas annulus around core 513, in Figs. 4 and 5, helps insulate the core 513 to retain heat and to operate more efficiently.
[0084] A general understanding of the principles described above will be facilitated by provision of an example with dimensions. Assuming that the arrangement of Figs. 4 and 5 was sized and configured for utilization with a medium duty truck having a horizontal exhaust system, such as a GM TOPKICK or a Chevrolet KODIAK, usable dimensions for the assembly 500 would be in general as follows: overall length between end cap 523 and end cap 552 about 35.5 inches (90 cm); overall length of internal shell 542 = 15 inches (38 cm); distance between end cap 523 and baffle 524 = 7 inches (17.6 cm); diameter of catalytic converter assembly 512 about 10.09 inches (25.6 cm); diameter of shell 502 about 11.09 inches (28.17 cm); distance between outlet end 536 of extension 533 and upstream face 517 of catalytic converter core 513 = 2 inches (5 cm); diameter of catalytic converter core 513 about 9.5 inches (24.1 cm); depth of catalytic converter core 513 = 6 inches (15.2 cm); diameter of inlet tube 520 about 4.02 inches (10.21 cm); diameter of outlet tube 560 about 4.02 (10.21 cm) inches.
(a) a muffler arrangement (500) comprising: an outer shell (502) having a first end,
a second end, an exhaust inlet (503) in said first end of said outer shell, and an
exhaust outlet (504);
(i) said muffler arrangement including a sound attenuation arrangement within said
shell;
(b) a catalytic converter arrangement (512) positioned within said muffler arrangement; said catalytic converter arrangement comprising a converter core (513) having an upstream surface (517) and an opposite downstream surface (518); said converter core having an outer periphery;
(c) an internal shell positioned within, and spaced from, said outer shell, to define
an exhaust gas flow annulus (544) therebetween;
(i) said converter core being operably positioned within said internal shell;
(d) said sound attenuation arrangement including a sound attenuator tube (556) having an entry port (557) spaced from said converter core downstream surface;
(e) an exhaust flow arrangement for directing exhaust gases through said catalytic converter arrangement, in a direction of flow from said upstream surface to said downstream surface, whenever exhaust gases operably flow through said muffler arrangement from said exhaust inlet to said exhaust outlet;
(f) an annular flow arrangement (544) for directing exhaust gases, after the exhaust gases have been directed through the catalytic converter core, in a direction past the converter core, and around an outer periphery thereof, in a direction of flow from the catalytic core downstream surface toward the catalytic core upstream surface;
(i) said annular flow arrangement directing flow of exhaust gases through said exhaust flow annulus and to said outlet;
(ii) said annular flow arrangement directing flow of exhaust gases into said exhaust flow annulus at a location between said sound attenuator tube entry port and said converter core upstream surface such that in use gases can, but are not required to, flow from said converter core downstream surface into said exhaust flow annulus without being directed through said attenuator tube; and
(g) said outer shell (502) being constructed and arranged with said exhaust gas inlet being positioned in said outer shell (502) at a location closer to said catalytic converter core upstream surface than to said catalytic converter core downstream surface; and, said outer shell (502) being constructed and arranged with said exhaust gas outlet being positioned in said outer shell (502) at a location closer to said catalytic converter core upstream surface than to said catalytic converter core downstream surface; said catalytic converter core being physically positioned between said outer shell (502) second end and both of said exhaust inlet and said exhaust outlet.
(a) a flexible insulation mantle (101) wrapped around said ceramic core; and
(b) a sheet metal casing (105) wrapped around said flexible insulation mantle.
(a) said porous core member is positioned within a distance of about 2 to 4 inches (51 mm - 102 mm) from said flow distribution arrangement.
(a) eine Schalldämpferanordnung (500), die umfaßt: eine Außenschale (502), die ein
erstes Ende, ein zweites Ende, einen Abgaseinlaß (503) in dem ersten Ende der Außenschale
und einen Abgasauslaß (504) besitzt;
i) wobei die Schalldämpferanordnung eine Schalldämpfungsanordnung innerhalb der
Schale umfaßt;
(b) eine innerhalb der Schalldämpferanordnung angeordnete Katalysatoranordnung (512); wobei die Katalysatoranordnung einen Katalysatorkern (513) mit einer stromaufwärts gelegenen Fläche (517) und einer gegenüberliegenden stromabwärts gelegenen Fläche (518) umfaßt; und der Katalysatorkern einen Außenumfang besitzt;
(c) eine Innenschale, die innerhalb der Außenschale und von dieser beabstandet angeordnet
ist, um dazwischen einen Abgasstromringspalt (544) zu definieren;
i) wobei der Katalysatorkern funktionell innerhalb der Innenschale angeordnet ist;
(d) wobei die Schalldämpfungsanordnung ein Schalldämpfungsrohr (556) mit einer von der stromabwärts gelegenen Fläche des Katalysatorkernes beabstandeten Eintrittsöffnung (557) umfaßt;
(e) eine Abgasstromanordnung zum Leiten des Abgasstromes durch die Katalysatoranordnung in eine Strömungsrichtung von der stromaufwärts gelegenen Fläche zur stromabwärts gelegenen Fläche, immer wenn beim Betrieb Abgase von dem Abgaseinlaß zu dem Abgasauslaß durch die Schalldämpferanordnung strömen;
(f) eine ringförmige Strömungsanordnung (544) zum Leiten der Abgase in eine Richtung am Katalysatorkern vorbei und um einen Außenumfang desselben herum in eine Strömungsrichtung von der stromabwärts gelegenen Fläche des Katalysatorkernes zur stromaufwärts gelegenen Fläche des Katalysatorkernes nachdem die Abgase durch den Katalysatorkern geführt wurden;
i) wobei die ringförmige Strömungsanordnung den Strom der Abgase durch den Abgasstromringspalt und zum Auslaß leitet;
ii) die ringförmige Strömungsanordnung den Strom der Abgase in den Abgasstromringspalt an einer Stelle zwischen der Schalldämpfungsrohreingangsöffnung und der stromaufwärts gelegenen Fläche des Katalysatorkernes leitet, so daß im Einsatz die Gase von der stromabwärts gelegenen Fläche des Katalysatorkernes, ohne durch das Dämpfungsrohr geleitet zu werden, in den Abgasstromringspalt strömen können, jedoch nicht müssen; und
(g) die Außenschale (502) so aufgebaut und angeordnet ist, daß der Abgaseinlaß in der Außenschale (502) an einer Stelle angeordnet ist, die sich dichter an der stromaufwärts gelegenen Fläche des Katalysatorkernes als an der stromabwärts gelegenen Fläche des Katalysatorkernes befindet; und die Außenschale (502) so aufgebaut und angeordnet ist, daß der Abgasauslaß in der Außenschale (502) an einer Stelle angeordnet ist, die sich dichter an der stromaufwärts gelegenen Fläche des Katalysatorkernes als an der stromabwärts gelegenen Fläche des Katalysatorkernes befindet; wobei der Katalysatorkern räumlich zwischen dem zweiten Ende der Außenschale (502) und sowohl dem Abgaseinlaß als auch Abgasauslaß angeordnet ist.
(a) einen flexiblen Dämmungsmantel (101), der um den Keramikkern gewickelt ist; und
(b) ein Metallblechgehäuse (105), das um den flexiblen Dämmungsmantel gehüllt ist.
(a) das poröse Kernelement in einem Abstand von ungefähr 2 bis 4 inches (51 mm - 102 mm) von der Strömungsverteilungsanordnung entfernt angeordnet ist.
(a) un agencement formant silencieux (500) comprenant : une enveloppe extérieure (502)
comportant une première extrémité, une seconde extrémité, une entrée d'échappement
(503) dans ladite première extrémité de ladite enveloppe extérieure, et une sortie
d'échappement (504) ;
(i) ledit agencement formant silencieux comprenant un agencement d'atténuation
de bruit à l'intérieur de ladite enveloppe ;
(b) un agencement formant convertisseur catalytique (512) placé à l'intérieur dudit agencement formant silencieux ; ledit agencement formant convertisseur catalytique comprenant une partie centrale de convertisseur (513) comportant une surface amont (517) et une surface aval opposée (518) ; ladite partie centrale de convertisseur ayant une périphérie extérieure ;
(c) une enveloppe intérieure placée à l'intérieur et espacée de ladite enveloppe extérieure,
définissant ainsi entre elles un espace annulaire (544) d'écoulement des gaz d'échappement
;
(i) ladite partie centrale de convertisseur étant placée de manière fonctionnelle
à l'intérieur de ladite enveloppe intérieure ;
(d) ledit agencement d'atténuation de bruit comprenant un tube atténuateur de bruit (556) comportant un orifice d'entrée (557) espacé de ladite surface aval de la partie centrale de convertisseur ;
(e) un agencement d'écoulement d'échappement destiné à diriger les gaz d'échappement au travers dudit agencement formant convertisseur catalytique, selon une direction d'écoulement allant de ladite surface amont vers ladite surface aval, chaque fois que des gaz d'échappement s'écoulent de manière opérable au travers dudit agencement formant silencieux, de ladite entrée d'échappement vers ladite sortie d'échappement ;
(f) un agencement d'écoulement annulaire (544) destiné à diriger les gaz d'échappement, une fois que les gaz d'échappement ont été dirigés au travers de la partie centrale de convertisseur catalytique, dans une direction passant devant la partie centrale de convertisseur et autour de la périphérie extérieure de celle-ci, dans une direction d'écoulement allant de la surface aval de la partie centrale de convertisseur vers la surface amont de la partie centrale de convertisseur ;
(i) ledit agencement d'écoulement annulaire dirigeant le flux de gaz d'échappement au travers dudit espace annulaire d'écoulement d'échappement et vers ladite sortie ;
(ii) ledit agencement d'écoulement annulaire dirigeant le flux de gaz d'échappement dans ledit espace annulaire d'écoulement d'échappement en un endroit situé entre ledit orifice d'entrée du tube atténuateur de bruit et ladite surface amont de la partie centrale de convertisseur de telle sorte qu'en service, les gaz peuvent, sans y être forcés, s'écouler depuis ladite surface aval de la partie centrale de convertisseur dans ledit espace annulaire d'écoulement d'échappement sans être dirigés au travers dudit tube atténuateur de bruit ; et
(g) ladite enveloppe extérieure (502) étant construite et disposée avec ladite entrée des gaz d'échappement placée dans ladite enveloppe extérieure (502) en un endroit plus proche de ladite surface amont de la partie centrale de convertisseur catalytique que ladite surface aval de la partie centrale de convertisseur catalytique ; et ladite enveloppe extérieure (502) étant construite et disposée avec ladite sortie des gaz d'échappement placée dans ladite enveloppe extérieure (502) en un endroit plus proche de ladite surface amont de la partie centrale de convertisseur catalytique que ladite surface aval de la partie centrale de convertisseur catalytique ; ladite partie centrale de convertisseur catalytique étant physiquement placée entre ladite seconde extrémité de l'enveloppe extérieure (502) et les deux dites entrée d'échappement et sortie d'échappement.
(a) un manchon isolant souple (101) disposé autour de ladite partie centrale en céramique ; et
(b) un gainage en tôle (105) enroulé autour dudit manchon isolant souple.
(a) ledit élément formant partie centrale poreux est placé à une distance comprise entre 2 et 4 pouces (51 mm à 102 mm) environ dudit agencement de répartition de l'écoulement.